Filed of Invention
The present invention relates to a prosthetic knee joint, more particularly, a prosthetic knee joint which enables high-angle flexion, has improved durability of the prosthetic components and also enhanced knee stability.
Knee arthroplasty, in which the natural knee is replaced with a prosthetic knee joint, is one of the most successful medical methods for remedying destructive knee-joint troubles.
U.S. Pat. No. 5,035,700 discloses a prosthetic knee joint which attains a high-angle flexion and is embodied, for example, as shown in FIG. 2, which schematically illustrates a fully flexed state. The prosthetic knee joint consists of a femoral component 1 consisting of implant metal, a tibial component 5 and a patellar component 20 consisting of plastics, e.g., polyethylene. The lower surface of the femoral component 1 is defined by the anterior erect portion 1a, the lower portion 1b and the posterior erect portion 1c, while each of these portions and the entire portions form a continuously smooth curved configuration. The femoral component 1 is provided with a peg 2 for securing it to the distal femur (not shown). The tibial component 5 has a concave surface 5a for enabling the femoral component 1 to slide thereon and is secured to the proximal tibia (not shown) with the stem 25.
The prosthetic knee joint proposed in the above mentioned U.S. Patent has a concave surface 1d at the lower central portion thereof, and the concave surface id is shaped to enlarge the maximum movement width of the prosthetic knee during flexion. It is described further the prosthetic components are configurated and dimensioned such that the quadriceps muscle tension approaches that in the natural human knee-joint throughout the full range of flexion.
Although not aiming at high-angle flexion, Japanese Examined Patent Publication No. 3-195,550 discloses the prosthetic components having virtually the same geometries as shown in FIG. 2.
The movement of the knee is not only a mere hinge action but also includes a swiveling action and a rolling action in the anterior and posterior direction. It additionaly includes a posterior rolling movement, which is essential in a high-angle full flexion, such that the contact between the femur and tibia displaces posteriorly and the axis of rotation also displaces posteriorly. Since the life style of Orientals frequently involves erect sitting position, the knee joint must be occasionally greatly flexed at high-angle flexion. It has been the practice to construct the prosthetic knee joint with an alumina femoral-component and a titanium-alloy tibial component with a bonded polyethylene top coating and to design the sliding surface between these components to enable high-angle flexion. However, when this prosthetic knee joint is fully flexed, the stress applied on the polyethylene top coating is greatly increased such that a danger arises of accelerated wear.